We propose a model of mitochondrial DNA organization in Zea mays of multiple, circular chromosomes of variable ploidy. Variant mitochondrial DNA organization correlates with whole organism male sterility and sensitivity to fungal toxins. Variant mitochondrial DNA organizations may be generated by chromosome rearrangements. We will study mitochondrial DNA organization by constructing a restriction endonuclease cleavage map of each chromosome, by electron microscopy, by hybridization of normal and variant DNAs, and by physical methods.